Buddyspace : Instant messenger with four novel twists: (1) it allows optional maps for geographical & office-plan visualizations in addition to standard ‘buddy lists'; (2) it is built on open source Jabber, which makes it interoperable with ICQ, MSN, Yahoo and others; (3) it is implemented in Java, so it is cross-platform; (4) it is built by a UK research lab, so it is 100% free with full sources readily available. Download

HipChat : HipChat is a hosted private chat service for your company or team. Invite colleagues to share ideas and files in persistent group chat rooms. Get your team off AIM, Google Talk, and Skype — HipChat was built for business. Free trial, Add code

IBM Lotus Sametime : Provides a core set of integrated real-time communications services—voice, data and video—that make it easy for people to find, reach and collaborate effectively with colleagues, customers and business partners. Installed

iGlance : Tiny program for talking and sharing over the internet. Download

Instantbird : A multi-protocol Instant Messaging client. Using it, you can connect to all your different IM accounts. Open source, Download